US2854267A

US2854267A - Shaft seals

Info

Publication number: US2854267A
Application number: US540104A
Authority: US
Inventors: Clifford A Stephens; Robert W Mccandless
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-10-12
Filing date: 1955-10-12
Publication date: 1958-09-30
Anticipated expiration: 1975-09-30

Description

Sept. 30, 1958 c. A. STEPHENS ET AL 2,854,267

SHAFT SEALS Filed Oct. 12, 1955 mm ,44 v

llli! mmlkk r States Patent SHAFT SEALS Clifford A. Stephens, Palo Alto, and Robert W.

McCandless, Redwood City,

Application October 12, 1955, Serial No. 540,104 3 tllaims. (Cl. 288-4 This invention relates to sealing devices, and more particularly to shaft and rod seals of the type employing leather as the pliant sealing material interposed between the relatively moving elements. It also relates to a novel composition of matter used to coat the leather element in shaft and rod seals. This application is a continuationin-part of our application, Serial Number 519,862, filed July 5, 1955.

Leather has long been favoredas far superior to most materials as a pliant sealing element for shafts, reciprocating rods and the like. Despite this, it is recognized that leather has certain disadvantages and fails to exhibit, to the degree desired, all the characteristics needed to meet the ever increasing requirements for a satisfactory seal. For example, leather varies widely in density, resilience, porosity and flexibility, all of which affect performance and suitability for use as sealing elements. Accordingly, over the years much effort has been directed toward improved processing procedures in an endeavor to provide a product of more uniform properties and longer service life. In addition, these attempts have included the augmentation of existing properties as well as the inclusion of new ones.

Another facet of the problem derives from the fact that certain desired properties of leather are customarily found only in combination with undesirable ones. For example, a leather having the desired flexibility is too soft to maintain good sealing contact with an eccentrically rotating shaft, or one which vibrates or whips as it rotates. Also, a flexible leather usually is quite porous. In consequence, it has a high reservoir capacity for lubricant, an advantageous quality. But this porosity is also attended by seepage of lubricant through the side walls of the leather, a highly undesirable quality. Previous elforts to seal the pores have destroyed the leathers capacity for storing lubricant and have stiffened the leather objectionably.

The primary object of the present invention is the provision of a seal utilizing as the sealing element specially processed leather in which the desirable properties of leather are retained and augmented while other new properties are added.

Another object is the provision of a sealing element having a main body of leather with a coating bonded to at least one surface and serving to seal that surface against loss of lubricant by seepage to reduce greatly the surface friction, to increase the wearing qualities, and to add to the mechanical strength of the leather but changing its stiffness only to a minimum degree.

Still another object is the provision of a metal-encased shaft seal having a flexible leather sealing element that is coated with a resilient covering confined to the surface area of the leather and effective to prevent seepage of oil through the side wall without interfering with the flow and storage of oil within the body of the leather.

Yet another important object is the provision of a shaft seal having a leather sealing element specially treated on its shaft-contacting surface with a low-friction coating resistant to attack by lubricants and having long wearing qualities, whereby the torque loss caused by the seal is reduced to a minimum and the service life is increased.

A further object is the provision of a technique for coating leather with a veneer of elastomer applied as a liquid and allowed to dry before the application of heat and pressure vulcanize the coating to the surface area of the leather.

Still another object is a mode of vulcanizing and molding a ring area only of a plaque of leather, whereby the unvulcanized center may be trimmed away and subsequently Vulcanized and molded in a difierent size and shape.

Yet another object is the provision of novel coating compositions suitable for sealing the surface of leather, textiles and the like and of imparting new and unique properties thereto in a simple, inexpensive and highly efiicient manner.

A further object is the provision of a leather sealing element with a film veneer which is soft, pliant, resilient, abrasion-resistant, which exhibits a much lower coeflicient of friction than the leather, and which does not sculf, ball up, blister or slufi ofi.

Numerous other objects and advantages of the invention will become readily apparent from the following detailed specification taken in connection with the accompanying drawings illustrating typical modes of practicing the invention, and wherein:

Figure 1 is a sectional view through a shaft seal in its installed position and featuring a leather sealing member provided with a low-friction protective veneer on its outer surface only;

Figure 2 is a fragmentary enlarged view through a similar seal but having a protective veneer on both of its surfaces;

Figure 3 is a fragmentary sectional view on a further enlarged scale, taken through the sealing member of Figure 2 and showing the thickness of the coatings on an exaggerated scale for illustrative purposes only;

Figure 4 is a sectional view through a mold used in molding the leather and vulcanizing the elastomeric surface veneer;

Figure 5 is a fragmentary view of the mold on an enlarged scale showing the mold closed against a plaque of leather; and

Figure 6 is an isometric view, partly in section, of the leather as it appears after removal from the mold.

Referring to Figure 1, it will be seen that the present invention may be practiced by incorporating our unique leather sealing element in a shaft seal of any suitable construction, such as the seal generally designated 10. The radial flange 11 of a specially prepared leather sealing element is clamped between a metal washer 12 and the radial flange of a cupped outer case 13, by means of a cup-shaped inner case 14. Thus, the in-turned edge 15 of the casing 14 is held pressed against the washer 12 by the curled-in rim 16 of the outer case 13. The exterior formed in the" bore wall.

cylindrical surface 17 of the outer case is accurately finished so as to have a snug press-fit with the side wall of a mounting bore 18 of a shaft housing 19. Seated I against the shouldered inner end 20 of the bore 18 is a suitable hearing, such as an anti-friction bearing indicated at 21. This bearing may be held seated in the bore, as;

by a split spring keeper ring 22, which seats in agroove The bearing'Zll serves to support a shaft 23centra1ly of the mounting'bore 18.

The flexible sealing member interposed between the shaft 23 and the seal casing is formed principally of leather and is, molded to provide an outer, radially extending, mounting flange 11 and a frusto-conical, axially extending, lip'flange 24. This general shape and form of leather sealing lip is conventional and'has been in common use for many years. The smallest diameter portion of its-inner edge 25 may be held insealing contact with the shaft 23 by a garter spring 26. V One of the'unique features of the sealing element is theprovision of a thin film or veneer 27 of a special elastomer bonded to the inner or shaft-contacting surface of the seal. If only one surface of the sealing member These substances, compounded along with a suitable solvent vehicle in a manner to be disclosed below, are applied in liquid form to the surface of the leather sealing member and then vulcanized.

' The elastomer does not penetrate beyond the base of the hair pore openings or of the surface crevices and other imperfections of the leather. This confinement of the veneer to the immediate surface area of the leather and its absence from the many voids in the body of the,

leather is highly important and has several advantages.

Thus, the absence of elastomer from the interior 'body of the leather permits of a free and natural capillary flow of lubricant within the leather in a path generally parallel to the inner and outer surfaces. Secondly, the many voids naturally presentin the leather are available as lubricant storage reservoirs. And, thirdly, the inherent flexibility of the body of the leather is not adversely affected by the presence of incompressible particles filling' the voids And, of special significance,'the exterior surface of the leather ,or the one in contact with the rotating shaft 23 is sealed by a thin film of resilient material which is'highly resistant to attack by lubricants, relatively impervious to both liquids and gases, and has a-coeificient of friction at least 50% lower thanthe identical leather sealing element without the surface coating of this invention.

A second embodiment of the invention is illustrated in-Figure 2 and differs from the Figure 1 design in that both sides of the leather sealing element have a surface veneer of elastomer. Thesame reference characters have been used as in the first'form'but are distinguishable by the use of a prime. The inner or flesh side of the sealing element is shown coated with a film of elastomer 28' corresponding to the coating 27' on the outer or hair side. The film thicknesses are somewhat exaggerated in the drawing since, in practice, a film thickness of 2 to mils has been found most elfective, Greater thicknesses can be employed but have a tendency to stiffen the leather objectionably and are not found to add to the service life of the sealing element to any material extent.

Coating both sides of the sealing element has certain advantages. It stiflens each side of the leather in equal degree; it provides a smooth finished surface on both sides of the sealing element; and it provides a substantially sealed reservoir for lubricant within the body of leather proper. The outer rim of this reservoir is sealed by the surrounding housing for the sealing element, leaving only the inner peripheral edge exposed to the interior of the appliance housing and the supply of oil therein. If the seal is to be used in a location not exposed to lubricating mediums, then the sealing element canbe saturated with lubricant before installation. Thus, in either mode of use, the sealin edge of the lip has'a continuous supply of oil available at all times. As soon as a film of' oil between the shaft and the contacting edge of the seal tends to disappear, it is immediately replenished from the supply stored by capillary action in the body of the seal. Furthermore, the low'friction coating in direct contact with the shaft contains a dry lubricant locked within the coating. This dry lubricant supplements the liquid lubricant within the body of the sealing element.

The coating compositions which we have found to be so satisfactory for surface films or

coatings

27,27 and 28 are'elastomers or rubber-like synthetics incorporating one or more dry lubricants that are dispersed therein to impart lubricity and other related properties important to a properly functioning seal. For example, the coating elastomer may be Neoprene GN or Neoprene GRT, stand ard elastomeric polymer of chloroprene commercially available from E. I. du Pont de Nemours '& Co. One hundred parts of this material should be compounded for rapid curing and mixed with between 10 and 60 parts by volume of a filling agent having lubricating properties such as graphite, molybdenum disulfide, mica or talc. (For graphite, the range by weight is between 20 and 120 parts perlOO'parts elastomer.) This mixture is dissolved in a suitable solvent to provide a low viscosity solution of 520%' solids. If a lower solids content is employed,

the film does not distribute uniformly to provide a reliably continuous veneer, while a solution of higher solids content is too viscous for satisfactory results. It will, of

course, be understoodby those skilled in the handling of elastomeric compositions that suitable curing agents, antioxidants and accelerators arerequired as usual.

Suitable solvents include a mixture of one or more.

aromatics (toluene, benzene, or xylene and homologues of them) with'paraifin hydrocarbons (e. g., gasoline or kerosene) or ketones (acetone, methyl-ethyl-ketone, and other liquids of the group) or naphthas. Wide variations of quantities can be used, and which solvent mixture is selected will depend on factors such as evaporation rate desired, cost, toxicity, etc.

"The following specific examples suflice to illustrate the relative proportions of constituents which have been found particularly suitable in artual practice:

EXAMPLE 1 V Neoprene rubber weight Another composition giving excellent results employs copolymers of butyl acrylate and acrylonitrile or ethyl acrylate and chloro-ethyl-vinyl ether in lieu of neoprene. Such a composition may be compounded as follows EXAMPLE 2 Polyacrylic elastomer Constituents: Parts by weight Lactoprene BA 12.5 (an acrylonitrile (87.5%

butyl acrylate (12.5%) copolymer) 100 Stearic acid 1 Sulfur 1 Triethylene tetramine 4 Graphite 80 Total solids 186 Methyl-ethyl-ketone 1504 Toluene 170 Total liquids 1674 Grand total 1860 A third composition makes use of nitrile elastomer instead of neoprene. The following is an example of components by weight found in practice to give excellent results:

EXAMPLE 3 Nitrile elastomer Constituents: Parts by weight Nitrile elastomer 100 Sulfur 2 Stearic acid 2 Zinc oxide 5 Phenyl-alpha-naphthylamine 2 Tetramethyl thiuram disulfide 0.5 Graphite 70 Total solids 181.5

Methyl-ethyl-ketone 1470 Toluene 164 Total liquids 1634 Grand total 1815.5

Still another composition which we have found to provide an excellent adherent veneer for leather employs chlorosulphonated polyethylene as a principal elastomeric 1 Kenflex BKenrich Corp.

In any of these four examples, mica, talc, and molybdenurn disulfide may be substituted for graphite, in equal volumes. Graphite is, however, preferred.

Any of the foregoing compositions may be applied to.

the leather by dipping, dripping, spraying or other common coating techniques. However, since the deposition of a layer of the desired thickness and uniformity requires contact with the liquid over an appreciable period of time, the dipping and dripping-spraying techniques are particularly advantageous. Dipping is only practical when it is desired to coat both surfaces of the leather, while spraying may be used to coat either one or both surfaces.

The dipping process may be carried out by immersing the leather into a tank of the composition while the latter is agitated to keep the solid constituents in suspension. Immersion should be continued for a period of 10 to 60 minutes depending upon the thickness of coating'desired. The leather is then removed and allowed to drain and dry at room temperature for a period of 6 to 24 hours after which it is ready for curing and molding to the desired shape.

The spray coating and dripping procedures will be obvious from the foregoing discussion of the dipping method. A spray, stream, or dripping of the coating liquid is applied to the leather for a period of 10 to 60 minutes. Care is, of course, exercised to distribute the coating composition evenly. lf a coating is desired on only one surface, the spray or stream is directed in such a manner as to exclude it from one side, and it may be dripped only on the upper surface. A preferred method is to carry a series of leather blanks or plaques along a conveyor, floating them on a film of the coating composition and passing them below a series of dripping stations, each of which may comprise a horizontal bar upon which the coating composition is being sprayed, so that it drips over the edges onto the blanks passing below. During the period of exposure, the flow of composition is discontinued and the pieces are allowed to dry preparatory to curing and molding which may be carried out by the aid of a mold of the type illustrated in Figures 4 and 6.

Figure 4 shows a 2-part mold closed against a plaque 40 of coated leather. The mold includes a lower female member 41 secured to a heated platen 42 of a molding press by means of a cap screw 43. The cooperating male mold member 44 is similarly secured to an upper platen 45 by a cap screw 46. It will be observed that each of the mold members has a

large area cavity

47, 47 which does not contact the central portion 48 of the leather plaque. The outer opposed surface areas of the

mold members

41 and 44 have complemental surfaces uniformly spaced from one another and shaped to form a sealing element of L-shape in section as clearly indicated in the several figures of the drawing.

The narrow

radial surfaces

49 and 50 of the mold members grip the center part of the plaque 40 firmly and depress it into the general cup-shaped form shown in Figures 4 and 6 and hold it in this shape while the leather take a permanent set and the elastomeric surface coatings are being vulcanized. The mold is closed under sufficient pressure to compress the leather from 2030% and so held for one minute while the molds are maintained at a temperature of approximately 275 F. It will, of course, be appreciated that the pressure, molding period and temperature may be varied over a considerable range as found to give the best results for the particular leather and coating composition being used. Molding may be carried out for longer periods (up to seconds) at lower temperatures, and shorter periods (down to 10 seconds) at higher temperatures, but temperatures higher than 325 F. should be avoided, else damage to the leather may result.

Slight curing of the coating opposite the

cavities

47, 47 of the mold members may occur from the limited amount of heat reaching this area of the coating composition. The mold is held closed for such a short interval that any curing which takes place will not interfere with the subsequent molding of a smaller sized sealing element from the discarded central portion ofthe plaque 40. This will behest understood by the reference to Figure 6 showing theplaque 40' afterit has been removedfrom the mold. The next stepisto' trim out thering of leather desired for the sealing member. This is accomplished by placing the seal in a trimming lathe and cutting away the unvulcan ized center along the conical surface indicated by a dotted line 50. The outer rim is likewise trimmed at an angle such as that indicated by a dotted line 51. The narrow flanged ringso produced forms the sealing element of the completed seal.

The salvaged central portion 48 of the disk may be. used to form radial-washer type seals or another cup-shaped sealingelement of the same general shape shown in Figure 2 but of smaller diameter. Hence, it will be selfevidentthat this molding technique avoids waste and permits maximum usage of a given plaque of leather.

We claim:

1. A shaft seal, comprising a housing ring adapted to be pressed into a fluid-tight fit with a housing bore; and an annular flexible sealing ring formed from sheet-leather stock, having a pair of side faces and an outer peripheral portion anchored to said housing ring with at least a portion of one face to contactthe shaft, and an inner peripheral portion slightly smaller in diameter than that of the shaft for which said seal is designed, said face of said sealing ring being sealed by a thin homogeneous layer formed principally of oil-resistant synthetic rubber vulcanized to the immediate juxtaposed surface region only of said sealing ring thereby leaving the body portion of said leather ring unobstructed by rubber stock and free for the capillary flow and stowage of lubricant.

2. In a metal-encased shaft seal of the type having a metal shell adapted to be pressed into a housing bore and to form a fluid-tight non-rotating connection therewith anda flexible sealing ring of leather having its outer rim anchored to said shell, said ring being shaped and arranged so that one corner of its inner rim is adapted to contact and form a running seal with a rotating shaft; that improvement which comprises a thin fluid-tight layer of flexible synthetic elastomer resistant to attack by lubricating mediums and impregnated with a dry non-soluble lubricant, said layer being bonded to that surface of said leather ring adapted to have contact with the shaft, said layer being confined to the area of the ring immediately adjacent the surface to which it is bonded.

3. In a metal-encased shaft seal of the type having a metal shell adapted to be pressed into a housing bore and to form a fluid-tight non-rotating connection there with and a flexible pre-formed sealing ring of leather ha ing its outerrim anchored to said shell, one corner of the inner rim of said ring being adapted to contact andform a running seal with a rotating shaft; that improvement which comprises a thin layer of oil-resistant elastomer having graphite dispersed therein, said elastomer being bonded to that surface of said leather ring in which the said corner of the rim is disposed and eflective to prevent the loss of lubricant by seepage from the surface of the ring to which said layer is bonded, said layer being confined to the area of the ring immediately adjacent the surface to which it is bonded.

4. A metal-encased shaft seal for providing a fluid-tight seal between stationary and relatively rotating members comprising: a rigid mounting ring adapted to have a press fit with one of said members and a leather sealing ring anchored to said mounting ring at one rim, a portion of one face near the other rim of said leather ring being adapted to press against the other of said relatively rotating members and forming a runing fluid seal therewith, said seal being characterized by the provision of a thin flexible low-friction surface-sealing layer of oil-resistant elastomer bonded to at least the said one face of said leather ring to prevent the seepage of lubricant therefrom without substantially interfering with the flexibility of the leather ringv or thelstowageuor. the 'flow therewithin .of

. 8 lubricant incontact with areasof said ring free of said sealinglayer. i i T 5. In a metal-encased shaft seal for providing a fluidtight seal between stationary and relatively rotating members and having a rigid'mounting ring adapted to have a press fit with one of said members, a leather sealing ring adapted to be anchored to said mounting ring at one rim, the other rim of said leather ring being adapted to press against the other of said relatively rotating members and form a running fluid seal therewith, said leather ring being characterized by theprovision of a .thin flexible low-friction sealing layer of oil-resistant synthetic rubber bonded to the hair side thereof and adapted to contact the shaft when installed in an operating environment, said layer being effective to prevent the..escape of lubricant through the exterior hair side of said leather ring without substantially interfering with the flexibility of the leather ring or the stowage or flow therewithin of lubricant in contact with areas 'of said 'r'ing'having no sealing layer bonded thereto.

6. A metal-encased shaft seal for providing a fluid-tight seal between stationary and relatively rotating members comprising; a rigid mounting ring adapted to have a press fit with one of said members, a leather sealing ring anchored to said mounting ring at one rim, the other rim of said leather ring having an axially extending lip adapted to lie against the other of said relatively rotating members and form a running fluid seal with the surface thereof, and garter spring means for holding said lip in contact with said relatively rotating member, said seal being characterized by the provision on its exterior hair side with a thin flexible low-friction sealing layer between about 2 and 5 mils thick of oil-resistant elastomeric materialimpregnated with dry lubricant, said layer being confined substantially to and intimately bonded to the surface layer on the hair side of the leather ring to contact the shaft, whereby the remainder of the ring is free to absorb and store lubricant while safeguarding against loss of lubricant by seepage through the hair side thereof.

7. An improvement in shaft seals of the type having a heat molded leather sealing ring encased in a rigid mounting case adapted to be pressed into a mounting bore surrounding a shaft; said improvement comprising a flexible oil barrier coating between 2 and 5 mils thick bonded to the surface area only of said leather on at least the side of said leather ring intended to face outwardly and to contact the shaft, said coating including as principal constituents a dry lubricant dispersed in an oil-resistant elastomer. 5

8. The improvement of claim 7 wherein said dry lubricant is chosen from the group consisting of graphite, molybdenum disulfide, talc, and mica, and wherein said elastomer is chosen from the group consisting of the polymers of chloroprene, nitrile, chlorosulfonated polyethylene, and acrylonitrile-butyl acrylate.

References Cited in the file of this patent UNITED STATES PATENTS 170,000 Weber et al Nov. 16, 1875 549,419 Wright Nov. 5, 1895 1,459,509 Knothe June 19, 1923 1,777,984 Quimby Oct. 7, 1930 2,114,908 Peterson Apr. 19, 1938 2,146,677 Johnson Feb. 7, 1939 2,248,761 7 Kosatka July 8, 1941 2,647,840 Oehler Aug. 4, 1953 2,700,623 Hall Jan. 25, 1955 FOREIGN PATENTS 526,552 Great Britain Sept. 20, 1940 OTHER REFERENCES 'Which Shaft Seal? (Rainey), published in Product Engineering, May 1950, page144 (copy in 288-3) (Div.